Reduce freemax values for dns_message mempools

Reduce freemax values for dns_message mempools

It was discovered that NAME_FREEMAX and RDATASET_FREEMAX was based on
the NAME_FILLCOUNT and RDATASET_FILLCOUNT respectively multiplied by 8
and then when used in isc_mempool_setfreemax, the value would be again
multiplied by 32.

Keep the 8 multiplier in the #define and remove the 32 multiplier as it
was kept in error.  The default fillcount can fit 99.99% of the requests
under normal circumstances, so we don't need to keep that many free
items on the mempool.